A thin, lightweight liquid crystal display is used widely as the display device for a TV receiver, personal computer, portable electronic device, etc. The liquid crystal display includes a liquid crystal panel to display an image and a backlight device which backlights the liquid crystal panel to improve sharpness of the image being displayed on the liquid crystal panel.
Many backlight devices use a cold cathode fluorescent lamp as a light source. Since the cold cathode fluorescent lamp uses mercury, however, if it is broken, for example, the mercury will possibly flow out and have an adverse influence on the environment. On this account, backlight devices using light emitting diodes (will be referred to as “LED” hereunder) have been proposed, one of which is disclosed in the Japanese Patent Laid Open No. 191311 of 1995, for example.
Also, the light emitting diode has a service life as long as about 50,000 hours. Therefore, use of light emitting diodes permits to reduce the adverse influence on the environment and implement a long-life backlight device.
However, LED is small in size. For example, its bottom has a circular shape whose diameter is about 9.6 mm and a height of about 6.09 mm, so that the light emitted from LED can cover only a limited range. Because of the narrow range of lighting, in case an LED-based backlight device is used to backlight a large-size liquid crystal display for a TV set, for example, it should include a plurality of LEDs disposed in array or plane. Many LEDs are necessary for this purpose.
However, use of many LEDs in the backlight device will add to the manufacturing cost of the backlight device and hence a large-size liquid crystal display including the LED-based backlight device will be expensive.
Also, the light emitted from LED varies in luminance from one LED to another. Therefore, the larger the number of LEDs used in a backlight device, the larger the variation in luminance and color of the light backlighting the liquid crystal panel will be. Any variation in luminance and color of the light backlighting the liquid crystal panel or the like will degrade color quality of an image being displayed on the liquid crystal panel.